FRIDAY, Dec. 21 (HealthDay News) -- There's been little change in global rates of infertility over the past 20 years, according to a new study.

In 2010, nearly 50 million couples worldwide were unable to conceive a child after five years of trying, according to the study published online Dec. 18 in the journal PLoS Medicine.

For the study, researchers examined 277 national surveys in order to estimate the infertility levels in 190 countries between 1990 and 2010.

The analysis revealed that in 2010, 1.9 percent of women aged 20 who wanted to have children were unable to have their first live birth (primary infertility), and 10.5 percent of women who had previously given birth were unable to have another baby (secondary infertility).

That works out to a total of 48.5 million couples worldwide, study leader Gretchen Stevens, of the World Health Organization, and colleagues explained in a journal news release.

Infertility levels in 1990 and 2010 were similar, with only a 0.1 percent decrease in primary infertility and a 0.4 percent increase in secondary infertility over the time period, the investigators found.

Primary infertility rates varied by region, ranging from 1.5 percent in Latin America and the Caribbean to 2.6 percent in North Africa and the Middle East in 2010. In general, country and global patterns of secondary infertility were similar to those of primary infertility.

"In the absence of widespread data collection on time to pregnancy, the methods used and results presented [in this study] provide valuable insights into global, regional and country patterns and trends in infertility," the study authors concluded in the news release.